Island



UNITED STATES PATENT OFFICE.

CHARLES E. W. DOWV, OF PROVIDENCE, RHODE 1$LAND, ASSIGNOR TO DARLING, BROWN & SHARPE, OF SAME PLACE.

PROTRACTO R.

SPECIFICATION forming part of Letters Patent No. 411,741, dated September 24, 1889. Application filed December 8, 1888. Serial No. 292,537. (No model.)

To all whom it may concern.-

Be it known that 1, CHARLES E. W. Dow, a citizen of the United States, residing at Providence, in the State of Rhode Island, have invented. a new and useful Improvement in Protractors,of which the following is a specification.

The object of this invention is to produce a reversible protractor that can be readily adjusted to the exact angle required, and that shall embrace in its structure great convenience, simplicity, accuracy, and durability; and it consists in the improved construction of the protractor, in the means for securing the arc of the protraotor within the circumscribing frame, and in the means employed for imparting movement of adjustment to the arc, as hereinafter fully set forth.

Figure 1 represents a face view of the instrument. Fig. 2 represents an enlarged detail section taken in the line in no of Fig. 1. Fig. 3 represents a side elevation of the adjusting-instrum ent.

In the accompanying drawings, A represents the exterior frame, provided with four sides a a, a a, which are arranged at right angles to each other. The central portion of the frame A is cut out in circular form, and the edge I) of the circular opening is provided with a groove 0, as shown in Fig. 2. The are E of the protractor, having the straight edges is k, is made to fit the circular opening 0 in the frame A, and is also provided upon its edge (1 with a groove 8, which corresponds with the groove c of the frame. When the sides of the frame A and the arc B at the edge of the opening 0 have been properly graduated, the two parts are to be placed together in proper position and a curved wire D passed into the opening formed by the opposite grooves c and e, as shown in Fig. 2, the opposite ends it of the wire abutting each other, as shown in Fig. 1, or being turned at the ends of the arc, as shown at 11' '13. The

parts A and B will thus be properly secured to each other, so that the arc B can be rotated within the opening 0 and cannot be moved laterally from the said opening, and by the employment of the curved attachingwire I am able to readily secure the arc B to a frame A, having four continuous sides a, without an opening through the same into the space 0. p

The frame A and are E are made of about the same thickness, and I provide the frame A with a series of holes f, and the are E with the holes g, the said holes f and g being adapted to receive the pins h h, which project from the face of the adj listing-lever E, by means of which the are 13 can be precisely and conveniently moved with reference to the frame A; and in the use of the lever E for this purpose the outer pin h maybe inserted into one of the holes f in the frame A, while the pin h is inserted into the hole g in the arc, the hole 9 being made to have sufficient looseness with the pin to permit the proper angular movement of the lever E to produce the required movement of the arc B, and in whatever position the hole 9 in the arc may be placed there can be an adjacent hole f for the proper insertion of the pin 7t.

It is to be understood that I do not limit my claim for the adjusting-holes to a frame A having four continuous sides, as shown in the drawings, as one of the sides or one corner of the frame may be cut away to the central opening, as heretofore in the construction of such instruments; and it is obvious that the series of holes f can be made upon the are instead of the frame, if desired; but I have preferred to make the same upon the frame.

I claim as my invention 1. A protractor having in combination a frame provided with a grooved circular opening and an are having a grooved edge and fitting the circular opening of the frame, with a Wire inserted into the groove between the are and frame, substantially as described.

2. A reversible protraotor having in combination a frame provided with a circular opening and with four sides at right angles to each other, and an arc fitting the circular opening and adapted to make a complete revolution Within the said opening, substanprovided with pins adapted to enter the holes tially as described. 0f the are and frame, substantially as de- 3. In a protractor, the combination, With a scribed.

frame provided with a circular opening and CHARLES E. WV. DOW'.

5 an .arc fitting the circular opening of the \Vitnesses:

frame, the frame and are being provided JOHN S. LYNCH, with adjusting-holes, 0f the adjusting-lever SOORATES SCHOLFIELD. 

